Alzheimer's disease (AD) is a progressive neurodegenerative disorder characterised pathologically by the deposition of amyloid plaques and neurofibrillary tangles, and neuronal degeneration, in the brains of affected individuals.
The major protein component of the amyloid deposits is a small 4 kDa peptide of 39-43 amino acids termed beta amyloid (β-amyloid or Aβ). Aβ, is a small protein thought to be central to the pathogenesis of AD. Numerous studies have suggested that Aβ accumulation and deposition may be critical to AD. The initial deposition of Aβ and growth of plaques has been suggested to occur via distinct processes. Aβ may either form higher oligomeric structures or remain in the monomeric form when it is deposited. In vitro studies have found that freshly solubilsed monomeric Aβ, at low concentrations, is not toxic to neurons in culture. However, after an aging period of several hours to days Aβ spontaneously aggregates in solution to form fibrillar entities that are highly neurotoxic. This suggests aggregation is a requirement for Aβ toxicity.
The AD brain has been shown to be under oxidative stress. Oxidative stress is a situation where there is an excess of oxygen free radicals or reactive oxygen species (ROS), which in turn damage surrounding tissue. Important ROS that damage the surrounding cellular components are the superoxide radical, hydrogen peroxide and the hydroxyl radical.
Superoxide dismutases (SOD) are metalloenzymes containing a redox-active transition metal (copper, iron or manganese) at the active site. SOD enzymes (SODs) dismutate superoxide radicals by electron transfer between superoxide anions and the transition active metal. While low levels of SODs do provide some protection by detoxifying superoxide radicals thereby preventing superoxide mediated cell damage, high levels of these enzymes sensitises cells to oxidative stress by the overproduction of hydrogen peroxide.
There is overwhelming evidence that supports the notion that the toxicity associated with human Aβ is largely dependent on its superoxide dismutase (SOD)-like activity and that this activity is copper dependent. These findings have led to the development of copper chelating agents for treating AD. However, whilst copper chelators may inhibit the SOD activity of Aβ, they are non-specific and the chelation of copper may disrupt essential biochemical functions in the brain and result in undesirable side effects.
Other diseases such as type II diabetes, Scrapie and Transmissible Spongiform Encephalopathies such as Creutzfeldt Jacob disease (CJD), variant CJD, Gerstmann Strausler Schinkler syndrome, Inclusion-Body Myositis and Bovine Spongiform Encephalopathy (BSE) have also been linked with SOD activity.
In PCT/AU02/01754 there is described a novel screening method involving phage display technology to identify novel peptides capable of inhibiting Aβ's neurotoxicity. Various phage libraries, each containing millions of peptides, were screened with random 6- or 15-amino acid sequences. After various rounds of panning, three sequences were selected.
The three candidate peptides (15merTNP, 6merPLP and 6merMTM) were examined to determine whether they could attenuate Aβ's SOD-like activity in vitro. A DCF fluorescence assay was used to assess the efficacy of these peptides on altering the production of physiological (brain) concentrations (200 nM) of human Aβ1-42. Results from these studies revealed that all three possessed the ability to modify Aβ1-42's SOD-like activity.
While the aforementioned research identified various candidate peptides that displayed an activity that attenuated Aβ's SOD-like activity in vitro, delivery of peptides to patients requires a biological agent that is a conformational match to the active site on the Aβ therein permitting attenuation of Aβ's SOD-like activity. Further, the amino acid sequence should preferably be as short as possible and confined in a structural manner that permits biological interaction while preserving maximum stability and longevity of the sequence in vivo.
The present invention seeks to provide an agent that ameliorates SOD activity and/or metal ion binding of causative agents such as Aβ. The invention further seeks to present efficacious treatment options for treatment of AD and other SOD related diseases.
General
Those skilled in the art will appreciate that the invention described herein is susceptible to variations and modifications other than those specifically described. The invention includes all such variation and modifications. The invention also includes all of the steps, features, formulations and compounds referred to or indicated in the specification, individually or collectively and any and all combinations or any two or more of the steps or features.
Each document, reference, patent application or patent cited in this text is expressly incorporated herein in their entirety by reference, which means that it should be read and considered by the reader as part of this text. That the document, reference, patent application or patent cited in this text is not repeated in this text is merely for reasons of conciseness. None of the cited material or the information contained in that material should, however be understood to be common general knowledge.
Manufacturer's instructions, descriptions, product specifications, and product sheets for any products mentioned herein or in any document incorporated by reference herein, are hereby incorporated herein by reference, and may be employed in the practice of the invention.
The present invention is not to be limited in scope by any of the specific embodiments described herein. These embodiments are intended for the purpose of exemplification only. Functionally equivalent products, formulations and methods are clearly within the scope of the invention as described herein.
The invention described herein may include one or more range of values (eg size, concentration etc). A range of values will be understood to include all values within the range, including the values defining the range, and values adjacent to the range which lead to the same or substantially the same outcome as the values immediately adjacent to that value which defines the boundary to the range.
Throughout this specification, unless the context requires otherwise, the word “comprise” or variations such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.
Other definitions for selected terms used herein may be found within the detailed description of the invention and apply throughout. Unless otherwise defined, all other scientific and technical terms used herein have the same meaning as commonly understood to one of ordinary skill in the art to which the invention belongs.